Receiver and wave monitor



March 16, 1948. M. G. CROSBY 2,437,910

RECEIVER AND wAvE MoNlToR Filed March 24, 1945 2 Sheets-Sheerl 1 hhbbhbbAAAAAAAAAAA VVVVVVVVVVV .TMILHIF ATTo/egvEY W2 W MW 2 SheetsSheet 2 Y BS O R C G. M

RECEIVER AND WAVE MONITOR Filed March 24, 1945 AAAAAAA VvE/v70@ Kurr/'ag Erosbg by ATTORNEY VVVVVV JAAAAAA VVVVVV atented Mar. 15, 19482,431,910 nEcErvER AND wAvE MoN'rron Murray G. Crosby, Riverhead, N. Y.,assignor to Radio Corporation of America, a corporation of DelawareApplication March 24,

1943, Serial No. 480,281

14 Claims. (Cl. 179-1715) This application concerns a new and improvedsystem for measuring phase modulation, frequency modulation andamplitude modulation on Wave energy. This system also provides means forindicating the frequency of a phase modulated wave and a frequencymodulated Wave and the amplitude of a carrier Wave which may beamplitude modulated.

In describing my invention in detail reference will be made to theattached drawings, wherein Figures 1a and 1b illustrates means forreceiving and amplifying phase or frequency or amplitude modulatedWaves, means for detecting modulations on said waves, and means formeasuring the modulation and the wave frequency during the reception offrequency modulation and phase modulation.

In the drawings, II! is a wave amplifier which amphi-les the Waveenergy, limits the same, and supplies it to an amplifier anddiscriminator circuit. The amplifier in Il may be of the tuned radiofrequency type, but in a preferred embodiment, comprises a radiofrequency amplifier RFA, a mixer or converter tube MT, a localoscillator O, and an intermediate frequency ampliiier I5 and amplitudelimiter LT all operating in a well known manner to amplify the receivedwave, reduce its frequency, and selectively amplify and amplitude limitthe Wave of reduced frequency. The oscillations to be used in tube MTfor beating against the received waves may be derived from a separatetube. In the preferred embodiment the converter MT is of theseparately-excited type Which has additional electrode 9 coupled toseparate oscillator energy fed to tuned circuit C1, L1, L1', L1".

The difference frequency or LF. is fed to circuit I3 and thence toamplifiers designated generally at I5. A highly stabilized oscillator Ohaving adjustable tank C monic generator HG is supplied and arranged tofeed oscillation over line CL' to grid 9 of tube MT. The circuit C1L1then serves as the plate tuned circuit of the multiplier I-IG. Anessential feature in the receiver IIJ is an amplitude limiter, whichwhen phase or frequency modulation is being received, removes from thewave energy` substantially al1 amplitude variations, and a preferredform of limiter including a double triode tube LT is used.

Although the amplitude limiter may be'of any approved type, I use alimiter of the type disclosed in my U. S. application, Patent No.2,276,565, dated March 17, 1942.

One of the triodes of this tube LT acts as a and L and feeding aharcathode-follower which drives thecathode of the Second triode throughthe common cathode resistance I1. This gives an amplier which limits thenegative peaks of the input wave by negative cutoff of the input tube.The positive peaks are limited by the negative cuto of the second triodesince there is a phase reversal eected by coupling through the cathodes.This gives a limiter which does not draw grid current over most of itsrange and which has been found 'capable of reducing amplitude modulationto a very low degree.

The output of the limiter is resistance coupled to the stage A tube andfeeds intermediate frequency voltage to this pentode input stage of thedetector unit through a low capacity concentric line CL. Y Y

A rectifying action takes place in the limiter tube which gives a changein limiter current read on the Limiter meter LMmounted in the detectorunit from about 2.6 milliamperes at the non-limiting input to 3.6milliamperes at. the limiting input. This current is the plate currentof the input triode of the dual triode. The voltage for this platecircuit is obtained from a separate connection I2 from the' detector(unit.

The limiter mustrbe so arranged that it may be removed from the'circuitor its limiting effect neutralized when amplitude modulated waves arereceived. In the preferred embodiment, the plate current for the firstvtriode of limited tube LT is supplied by lead I2, connected with switchS3 in the discriminating detecting andmetering system which follows theapparatus and circuits in i0, in all positions of switch S3 except thatlabeled AM. When amplitude modulation is being received,V the lead I2 isinterrupted so' that the plate of the first triode inA limiter tube LTgets no plate voltage. The limiting action is stopped. However, thecapacity feed through the electrodes of the tube LT in the limiter issufficient to couple the intermediate frequency amplifiers through thelimiter to the grid of the amplifier tube in stage A by way of a copperpipe concentric line CL and coupling condenser I6.

Stage A is a conventional pentode amplifier with its anode connected tothe high potential end of atuned circuit 20, the other end of which iscoupled to a second tuned circuit 22, the lower end of which 'is coupledto ground by coupling condenser 30. Plate potentialV for the anode oftube A is supplied by the inductances of circuits 20 and 22 from thesource of plate current including the filter 26. The screen gridelectrode is alsosupplied by'current through this same connection.Circuits 20 and y22 form a Mountioy shaft as Sl and S3, has fourpositions, one of which is off and another of which (marked AM) is usedwhen amplitude modulation waves are being received. When the switch ison AM, an amplifier gain adjusting potentiometer 66 is included in shuntto the grid biasing resistor 61.

When the switch S2' is on PM and phase moriulation is being received,the resistor 61 is shunted by a condenser 69. The purpose of thiscondenser 69 and resistance 65 is to modify the modulating potentialsbeing amplified to correct the their anodes coupled together byresistors iiiv and 40 with the sistors connected to ground. the diodes Band C are likewise coupled by resistors 4| and 4| of equal value. 4Theresistors 4i anode end of one of the reand 4| are shunted byradio-frequency by-passing condensers.

'Ihe high potential end of the series resistors l 40 and 40 is connectedto a contact on the switch Si marked PM, the latter contact beingconnected 'to a second contacten Sl marked FM, these being the switchpositions when phase mod-l ulation 'or frequency modulation is beingmonitored.

The cathode of the 'diode B is coupled to a switch 'contact marked AM.This contact is used when amplitude modulation is being received and thepotential drop in 4I 'and 40' in series appears on the contact Since thecircuits and 22 are of the off-tuned type and are coupled differentiallyt'o the rectiers, wave length modulation at zero modulation or carrierfrequency produce's across the resistor 40 and 40 equal potential dropsvwhich neutralize or cancel each other. When the carrier deviates in onedirection, the potential at PM and FM becomes negative. When 'thecarrier devlates 'in the 'opposite direction, 'the potential at PM andFM becomes positive.

As to the reception of amplitude modulation note that the 'resistor '41connected 'to the cathode of diode B is in series with 'the resistor 40connected 'with the'grounded anode of diode C so that 'as to 'amplitudemodulation, that is', when the carrier waxes a'nd wanes in intensityrather than 'shifting in frequency, a corresponding change in `thedirect current 'in both diodes is produced and 'the sum of thepotentials produced in resistor 40 and `40, considered in series,appears at AM.

Switch SI 'has 'an'arm connected 'by a 'filter resistor 50 tobuifer'afmplier'tube D `of thecathode 'follower ty'pe. The 'anode ofthis 'tube D is connected to ground by bypassing condenser'52 andthrough a filtering resistor 53 to the same direct current supplymentioned above. The cathode of tube Dis connected to ground 'by a fixedresistor 56 51 and a tuning indicator meter -43. This 'tube and meteralso serves 'as a volt meter, during the reception `of 'amplitudemodulation. The cathode end of resistor, 56, wherein the modulationpotentials as'amplifled are set up, is coupledby a coupling condenser'toa contact marked Use to be 'fed by 'way "of 'switch 59 and at'-tenuating resistor B0 'and calibrated scale potentiometer v62 to the'rst 'stage of a resistance and capacity coupled Yhigh gain ampliercomprising stages E, F. G, and H. -Th'eresistance coupled 'amplier is'substantially 'conventional lbut is unique in the 'following'respectszThe output of stageE is fed by aeoupling'con-A denser and series'resistor 65 'to the grid of 'the stage 'F. The'swit'ch S2,`which'is onthe same The cathodes of distortion caused due to the fact that phasemodulated wave is being received on a frequency modulation receiver.This network comprising resistor 65 and condenser '59 when taken withtube input and output and circuit capacities and resistor 61, is suchthat the higher modulation freanda potentiometer resistance quencies.are attenuated.

More exactly, the modulation frequencies are attenuated substantiallyinversely in accordance with their frequency. Further information as tothe purpose of this correcting network has been set forth in detail inmy U. S. Patent No. 2,230,212.

When the switch S2 is moved to the point FM for the reception offrequency modulation, the amplifier overall gain control resistor 68 isincluded in shunt to the resistor 61.

The stage F has its anode coupled by a condenser and gain adjustingresistance including potentiometer 15 to the grid of the stage G. Aswill be explained hereinafter the overall gain of theamplier E, F, G, His set by adjusting potentiometer 15, and this gain control is used tocalibrate the system when phase modulation is to be amplied.

The Afinal stage H of vthis amplifier of controllable gain, the gain ofwhich is calibrated as will appear more in detail later, is coupled by atransformer 13 to a meter 14. On this meter 14 the extent of modulationof the wave energy being monitored is indicated. The output, here 600,ohms, is also supplied to jacks'into which phones or cathoderay tubes orother utilizing means may be plugged. A damping resistance 19 isarranged to be switched in shunt to the secondary winding of the'transformer 13 when Calibrating the system with the load removed fromthe output jacks.

`The resistance' in the cathode circuit of tube D is also'coupled to ajack'5l into which an oscilloscope may be plugged to show directly thefrequency modulation wave form of the `discriminatoroutput ahead of theaudio amplifier.

This receiver and monitor is calibrated to measure the degree o r depthof phase modulation in decibels above or below a deviation` of oneradian. This inculdes the measurement of the depth of phase -modulationused for frequency diversity in telegraphtransmitters. My system is alsoarranged to 'measure frequency lmodulationV vin cycles and frequencymodulation FM decibels below a predetermined value'of deviation.Deviation as used here is departure to one side only o'f theunmodulatedphase or frequency. The system also-measures amplitudemodulation in decibe'lsbelow"100% modulation.

"I he indicating device, from which the reading 'of the depthofmodulation is taken, is calibrated potentiometer l62. Thispotentiometer is calibrated in decibels. In reading a degree ofmodulation, 62 is set'to 'the value which givesea full scale reading on'meter 14. Thereading. of 62 then reads directly 4.the number ofdecibels which the measured modulation isfhelow the predeterminedvalues.

A primary object of this receiver is Lto measure phase modulationlevels, such as, measuring hum modulation calibration of the modulationinput and the like. Y

The receiver is a revamped communications receiver in which provision ismade to replace the oscillator therein by an external high frequencyoscillator because the internal oscillator was too susceptible tomicrophonics during the measurement of low levels of phase modulation.

The special high-frequency oscillator O had to be added on account ofthe high susceptibility of the ordinary oscillator to phase modulationmicrophonics. The microphonics are introduced as a frequency modulationdue to the vibration of condenser plates, wiring and tube elements. Whenthis frequency modulation is received on a phase modulation detector,the eifective phase deviation is extremely high for a degree offrequency modulation which would not be objectionable on a frequencymodulation detector. The reason for this is that the effective phasedeviation of a frequency modulated wave is inversely proportionalquency. Hence, the lower the modulation frequency, the higher is theeifective phase deviation. Consequently, the effective phase deviationof low frequency shocks or'vibration of the os cillator components mayproduce an eective phase deviation which is only a few decibels belowthe full modulation of one radian or 57.3 degrees.

Four measures were applied to reduce the microphonics: First, and mostimportant, was the increase of the fixed capacity of the oscillatortuning condenser C. Increasing it 100 times decreased the microphonicsabout decibels. This change made the microphonic components of thetuning a small part of the whole capacity so that the microphonicvariation was a reduced percentage of the tuning capacity. Second, thewiring and parts were mounted as rigidly as possible to reduceVibration. Third, an investigation into the capacity microphonism oftubes was conducted so as to be able to choose a tube with low capacitymicrophonism. Fourth, the shielding box was made heavy to avoidvibration and it was mounted with rubber shock absorbers.

The frequency range of the oscillator which is of a modified Hartleytype is a single xed range of 5.8 to 10.2 megacycles. The oscillatorfeeds a harmonic generator H. G. which generates second and thirdharmonics to cover the ranges from 10.2 to 18 megacycles and from 18 to31 megacycles respectively. The plate tuned circuit of the harmonicgenerator consists of the tuned circuit C1, L1, Li' and L1" of theoscillator portion of the detector MT (which may be a 12H8). When theexternal oscillator O is used, the plate end of the oscillator coil isconnected through the concentric transmission line CL' to the plate ofthe frequency multiplier tube HG in the eX- ternal oscillator. At thesame time the plate connection of the tube MT is connected to the screenvoltage source. The filament of tube MT is connected to a source ofrectified direct current to eliminate frequency modulation humintroduced when this tube is used with the internal oscillatorconnection.

In this receiver, C2, La is tuned to the signal frequency, C1, L1 istuned to the signal frequency plus or minus the intermediate frequencyand C, L is tuned either to the same frequency as Ci, L1 or to asubharmonic of that frequency. For example, if the signal frequency is10 megacyto the modulation fre.

cles and the intermediate frequency 450 kilocyf cles, C2, Lz is tuned to10 megacycles, C1, Lr to 10.45 or 9.55 megacycles, and C, L to 5.225l or4.775 megacycles. For this example, the second harmonic of theoscillator is chosen.

The use of the harmonics of the oscillator in place of a tap switch tochange the range, has the advantage that the tuned circuit of theoscillator may be made more solid so as to reduce microphonics due tovibration. The susceptibility to microphonics is also reduced by makingthe fixed capacity, Cf, of the tuned circuit unusually high. This causesthe variable capacity, which is susceptible to vibration, to be a smallpart of the whole capacity and thereby have less effect on the frequencyof'the tuned circuit.

With such a large value of fixed capacity on. the tuned circuit,variation or tuning requires a. large change in capacity. This isaccomplished by the numerous steps of capacity available onv capacity C.

The intermediate frequency output (455 kc.)- is fed by 4a copper pipeconcentric line from theplate of the limiter tube through the condenserIS to the grid of pentode kA in the detector unit'` which was builtseparate from the receiver. The. plate circuit of stage A feeds adiscriminator circuitsomewhat similar to' the discriminatordisclosed inMountjoy, U. S. Patent No. 2,280,536, issued April 21, 1942, butmodified in such a manner as to make available at FM and' PM either thefrequency modulation or phase modulation differential outputs or theamplitude modulation series-aiding combination at AM.

The outputs of the detectors B and C are fed through a switch Sl to thegrid of a cathode follower triode D. Tube D serves as a Vcombinationtuning indicator, detector volt'meter for the AM connection and buffertube to feed the low impedance attenuator network including 62. Thecathode current of tube D is adjusted so that with the switch SI in theoff position marked Oli the tuning meter 43 reads .5 milllampere. Thenfor the PM or FM connection, the tuning is adjusted for this mid-scalereading of .5 milli AM connection the input level.

ampere. For the is adjusted for .7 milliampere. Potentiometer 5l markedZero adjust is the variable cathode resistor and is used to adjust theoutput of D for Zero center indication in 43.

Tube E is the first audio amplifier. The tap switch S2 in the gridcircuit of the second audio amplifier F switches in either theintegrating network including condenser 69 or the potentiometers 65 or68 for adjusting the calibration of the AM or FM detection. Theintegrating network is composed of resistor 65 connected to the grid oftube F and condenser 59 connected between ground and the PM contact ofthe tap switch. The potentiometer for adjusting "the calibration of thePM detectlonis potentiometer 15 in the output of tube F and in the gridcircuit of the third audio amplifier tube G. This potentiometer adjuststhe gain for all the types of detection since qit is in the commonoutput circuit. Normally, it will be the only one requiring adjustument. It should always be set prior to the adjust ment of the AM or FMcalibrations.

The calibration of the receiver depends upon the maintenance of constantdetectorv current, constant discriminator sensitivity, and constantaudio amplifier gain. The detector current is maintained constant FM andPM connections and by manual adjustby the limiter-LT for the.

ment for the AM'connectin. The discriminator sensitivity maybe assumedt'oreman "constant after the original calibration. The audio'aiplifiergain is maintainedfconstant by the calibration adjustments.

The audio ampli'er gain is 'calibrated with 60 cycles A. C. from ahired-'potentiometer 12, 14 fed by the lament voltage. This Afixed'voltage is switched to the input of the attenuator "by throwing the UseCal. switch 549 to Cal Originally, it was planned to adjust the'valueofthe Calibrating voltage to a fixed amount 'by means of anadjustable p'otenti'oin'ete'r and a voltmeter VM. However, it wasfoundfthat the calibration remained more constant whentheca'libratingvoltage was allowed 'to varywith the lline voltage. Hence the adjustingpotentiometer was removed and the iixed potentiometern. 14iised.

In calibrating mym'eter a phase modulation calibration should be maderst because the gain of the amplifier for the AM and FM 'cndi'- tion, asWell as for the PM setting. This potentiometer 15`is the sole adjustmentfor PM, whereas potentiometer B adjustsv for AM and poten*- tiometer 68adjusts for FM.V

To calibrate the receiver, I-put on 'I 0 'or-impress at I6 a carrierphase modulated b'ytonea'nd of'a known extent of modulation. Zero centerreading for the tuning meter is setl by putting'S'l (note thatS21andS3`on the network 60 and.62. The switch Oni is.

closed to shunt the open `jacks vby damping. rel

sistance 15 and 11 is closed to putfvoltmeterlil.

across transformer` 13. The attenuator network including 62 is nowset'atzero db; reading, which corresponds to maximum attenuation. of.thexexcitation supplied tor E. Potentiometer 15 isn'ow adjusted for ful1scale readingy on meter 14 placed in circuit by closing 11..

I then throw switch 59 to the contactlabeled Cal. therebyy feeding intothev inputwof-.tube'E a small 60 cycle A... C. voltage. derived from thefiilament winding. of `aftran'sformer, one side 'of which' Winding lead1| to the network 122a`nd-14 Y sideof which Winding is grounded. Asmallpor tion of this A. C. voltage is vied to the attenuator network 60and-62' and thenceto the input'of Vthe amplier.

Attenuator network. potentiometer 621 is'A tlfenv adjusted and read fora f'uil scale reading on modulation (volt) meter setting ofpotentiometer 62 bodiment this reading was -1'0.5.`db; for ap'haeedeviation of one radian) and in'iutu're PM calibrations of the audiofrequency ampl'iiir E, F,

potentiometer 62 is. set. at this. noted. setting,

and potentiometer 15 readjusted` for fulllscal` reading onmodulationzmeterJll This procedure adjusts the gain 'o'fv 'the "ampliLgainA adjustment potentiometer 15 adjusts the overallis coupled. byl andthe other inthe 'original calibration with a tone modulated Signal.

To 'calibrate for FM we follow the same procedure except now switchesSL'SZand S3 areo'n FM. Energy modulatedV a vknown amount in frequency'by tonev is applied to the receiver or introduced in the input of tubeA. Moreover, wheni'is thrown to Use and 62 is set at zero db. readingona scale which corresponds tonearly maximum attenuation, potentiometer 68is adjusted for full scale reading on meter 14 instead of potentiometer15 as in the prior procedure followed in the case of phase modulation.This reading of G2 is noted for future calibration purposes. Again theswitchfi!l is put on Cal and attenuation network 62 is adjusted for fullscale reading on meter 14. The calibration reading on the scale of 62 inan embodiment was 38.5 db. for 'a frequency deviation `of 3000 cycles.

Tmonitor an amplitude modulated wave the switches SI, S2 and S3 arethrown to AM and the receiver is arranged and adjusted for a givenreading on meter 43 by adjusting the gain controls in the receiver of10. The limiter in the receiver is/als'o rendered ineiective in themanner described hereinafter. In the arrangement shown, switch S3removes the anode potential from one of the triodes in limiter LT at there'- ceiver, while the capacity `coupling in the limiter tube'issuilicient to feed the amplitude modulated I. FL to the followingstages but no limiting takes place.

To 'calibrate the amplifier E, F, G and H, for monitoring amplitudemodulation, after the switch 59 is put on' "Use and the attenuator 62 isadjusted for rero db., gain contr-0l potentiometerJG. is adjustedy forthe full scale modulation reading on meter 14. Then as before the switch59-is placed on Cal and pad 62 adjusted for full 'scale modulationreading on meter 14. This reading of 62 is noted for future calibrationpurposes.

It will be noted that the attenuator 62 and meter 14'are calibrated toread directly in decibels below zero level. In one embodiment zero levelcorresponds to a full amplitude modulation, at 400 cycles tone, 3000cycles frequency module tio'n on 400' cycle tone, and one radian or peakdeviation. The amplifier vgain for this adjustment is obtained byadjusting potentiometer 15 first for PM'then G'Sfor AM and 68 for FM.

During the monitoring of amplitude modulation, the output lof the diodesB and C'is not differential .and there is a steady D. C. output whichcorresponds to carrier strength and this carrier strength is recorded ornoted by giving th'e needle on the meter 43 a slight deflection abovemid-scale reading.

4The system is now ready to investigate the modulation on phase orfrequency or amplitude modulated waves depending on which type ofmodulation it has been calibrated for. When' PM monitored the switch S2includes condenser 69 inA shunt to resistorl 2| to correct the audio,which is distort'ed'due to the fact that the PM is received on a'nFMreceiver.

Irl-monitoring FM, we adjust 62`f0r full scale reading on 14 and readthe db. value on the scale of G2. 62 is calibrated in decibels. Forinstance, if the reading were -6 db., the depth o'f modulationV would be6 below full modulation. If the calibration has been for PM the saine`procedure is followed; For- AM the reading is again taken on the scaleo'f62lwhich is adjusted for 715' full'scale' readingfo'ni meter 1'4.'

The meter 43 is calibrated in cycles and indicates the frequency of thereceived wave when FM and PM are monitored. The meter 43 is alsocalibrated for carrier intensity and indicates the same when amplitudemodulation is received. As stated above, the hand is' given a deflectionabove the mid-scale reading.

When tuning in signals that are quite strong, care must `be exercised toavoid tuning to one of the spurious responses consisting of the harmonicbeat points. These points are composed of the beat between harmonics ofthe signal and of the local oscillator. For instance, the secondharmonic of the signal may beat with the second harmonic of the localoscillator to cause an intermediate frequency in the same manner as thecorresponding beat between the two fundamentals. The harmonics areself-generated in the detector and are especially noticeable when thedetector is overloaded. When a signal is tuned in by this harmonic beatmethod, distortion is produced in the case of amplitude modulation1while in the case of frequency and phase modulation the frequency orphase deviation of the incoming signal is multiplied by the order of theharmonic that produces the beat. Thus, if the beat between the secondharmonics -of the signal and oscillator were tuned in, the phasedeviation would be multiplied by two so that readings would be 6 db.high.

These harmonic beat points all occur in the tuning range between the twofundamental tuning points which are produced by the oscillator being onthe highand low-frequency sides of the signal, respectively. Forinstance, if with the oscillator on the high-frequency side of thesignal, the dial reads 60 for the fundamental tuning point, and with iton the low-frequency side of the signal, the dial reads 40 for the otherfundamental tuning point, all of the harmonic beat points would occur inthe range between 40 and 60. This feature furnishes a means for avoidingthe harmonic beats. By tuning to the highest or lowest one of the group,one of the fundamentals will be obtained. The harmonic beat points areusually weaker than the fundamental points and fall off very rapidly asthe signal input is reduced.

The following procedure may be used for measuring the degree of phasemodulation on a keyed telegraph signal. For this type of observation,the receiver' should be switched to FM. It has been found that there isless trouble from key thumps when the FM connection is used. It. ispossible to use the FM connection to measure phase deviation where themodulation frequency is known and where the modulation is fairlysinusoidal.

The 600 ohm output must be first fed to an oscilloscope and theoscilloscope deflection calibrated against the output meter 14 reading.The oscilloscope furnishes an indicating device which will allowreadings to be taken during the mark period and will not be held oiscale by the toutput during the space period. To calibrate theyoscilloscope, a 400 cycle tone may be fed through the amplifier E, F, G,and I-I by plugging the output of -a beat-frequency oscillator in thejack marked Scope input. The output of the receiver may be switched offby turning down the I. F. gain controls. The attenuator Sii, 62 on thedetector unit, or the output yof the beat-frequency oscillator may bevaried to give a reading of zero on the output meter 14. The sensitivityof the oscilloscope may then be set to give a given de'-,

VAing the potential drop across one y named impedances and one of saidying circuit and connections for applying flection on the screen. Thisdeflection will correspond to zero db. on the output meter so that themeter may be switched olf and the oscilloscope may now be used in placeof the output meter 1li.

With the loscilloscope calibrated as an indicator, the readings of thefrequency deviation may be taken in the normal manner except that theattenuator is adjusted for the given reading on the oscilloscope insteadof on the output meter. Some signals will be rather difcult to readowing to the n-oise and interference that is brought up by the limiterin the space intervals. Aural observation of the keying will aid inmaking the reading. It will be found that key thumps are the leasttroublesome when the tuning is very carefully done.

When the reading of the phase modulation has been obtained as a degreeof frequency modulation, the frequency deviation may be converted to aphase deviation by the application of the relation:

in which 0 is the phase deviation in radians, Fd is the frequencydeviation in cycles, and Fm is the modulation frequency cycles. Forinstance, let it be assumed that the reading of the attenuator toproduce the given deflection on the oscilloscope is -20 db. Fullmodulation for the FM setting of the receiver is a frequency deviationof 3000 cycles. Hence the frequency deviation is 300 cycles. Let it alsobe assumed that the modulation frequency of the phase modulation thatwas being measured was 600 cycles. The phase deviation in radians wouldthen be 30D/600 or 0.5 radian by application of the above-mentionedrelation. Hence, the phase deviation would be 6 db. below one radian ora reading of -6 db. if it were measured on the PM connection of thedetector.

I claim:

1. In a system for deriving modulations from wave energy modulated inphase or frequency or amplitude, a modulated wave energy detectorcomprising a frequency responsive circuit energized by said wave energy,a pair of diodes having anodes and cathodes differentially coupled tosaid frequency responsive circuit, a pair of impedances in seriesbetween said anodes, a pair of impedances in series between saidcathodes, and connections for deriving the potential drop across saidfirst-named series impedances when phase or frequency modulated wavesare being received, and connections for deriving the potential dropacross one of said first-named impedances and one of said second-namedimpedances in series when amplitude modulated waves are being received.

2. In asystem for analyzing wave energy modulated in phase or frequencyor amplitude, a modulated wave energy detector comprising a frequencyresponsive circuit, a pair of diodes having .anodes and cathodes coupledto said circuit,

a pair of impedances in series between said anodes, a pair of impedancesin series between .said cathodes, connections for deriving the potentialdrop across said first-named series impedances when phase or frequencymodulated waves are being received, connections for derivof saidfirstsecond-named when amplitude modulated measurone of impedances inseries waves are being received, a modulation 11 said derivedpotential'sfto saidy modulation measuringf circuit.

3j In afsyste'm-forI relaying w'a'vcl energy the amplitude orinstantaneous frequency ofvwhich is-varying,two'electr'or'ffdisehargevsystems each including input electrodes'including'fa control grid and output electrodes'V including 1 anelectron receiving electrode and a-sourcevofelectrons; a couplinglbetween .the output electrodes -of one'of said systems and theinputelectrde's of the other system, connections# for v impressing thewaves to be' relayed onthe"input electrodes of said'one of said systems;connections for deri'ving relayed wa'tve'energyl 4fromtheoutput'electrodes ofthe said-'other oi'said'systems'connections forsupplying operating potentials tothe electrodes of said systems wherebythe amplitude of said wave energy being relayed is' limited; and meansfor interrupting said supply to the elec'- tron receiving electrode ofvone of saidy systems if the relayed wave energy is modulated inar'npli'-tude so that substantiallyno limiting of the wave energy amplitude takesplace in the relaying system.

4. In a systemlfor relaying'wave energy modulated in amplitude or as fto instantaneous frequency in accordance with signals,` two electron"discharge systems each including a'source of d electrons,r a .controlgrid andV anv anode; a cornmon impedance connected between thecontrolgrid and electron. source' of" both systems,con nections for impressingthe modulated waves to be relayedon the control grid and cathode of "oneof said systems, connections'for'derlving relayed wave 'energy from theanode andcathode'of the other of said systems, connectionsforsup'pl'ying potential to the anode of said one of said systems ifthe' instantaneousAV frequency of the relayed wave energy is modulatedso that wave* energy amplitude limiting takes place in thejrelayingsystem, and apparatus for interruptingA said supply if therelayed wave energy is modulated in amplitude so that relaying of `saidwaveenergy without amplitudeV limiting tales place;

5, Ina systemv for relayingjwave energy-the.

ins'tantaneous'V frequency or the amplitude? of whichA is' modulated Yin accordance with-signals, two electron discharge systems eachhavingin'put and output electrodes, including-a sourcefof electrons,acommon impedance connected between electrodes of said systems,connections for im`- pressing the waves to be relayed on theinputelectrodes of one of said systems, connections for deriving relayedwaves from the output electrodes of the other of saidsystems,sc`onnections for supplying operating potential to-'tlie-anodeelectrodes of said systems to limit the amplitude of the wave energybeing relayed, and means for interrupting said supply to at least'soneanode electrode if amplitude modulated waveenergy is being relayed topreventv amplitude limiting of the wave energy being relayed.

6. In a modulation meter adapted teana'lyae wave energy modulated inphase' or frequency? or amplitude, a` f requencyresponsive circuit;yconnections for impressing saidfwave energy ther'ebn, two rectierscoupled to said' frequency respb'nsive'lcircuit, impedances connected tosaidr'ectiilers' for combining the rectier outputsdiffe'rentially whenphase or frequency modulated Waves are being received or additively whenamplitude modulated waves are being received, ari amplifier includingamplifier gain control means andamodulation potentialcorrectingfnetworkv that Amay be switchedin or'out andhaving 12 anoutput coupled tota meter and connections for applying the vdifferentialor the additive output ofA 'said impedances to said amplifier.

7. Inla-system 'for demodulating wave energy the-amplitude orinstantaneous frequency of whicnis varying, afrelay` tubeV excited bysaid modulated wave energy, connections to said tube foi-Yop'erating`the same :as an amplitude limiter when* tlievwa've ism'odulated in phaseor frequenoy or' as aicoupling tube only when the wave energ'yisamplitude modulated, a detector comprising'a'pair. of diodeshaving adifferential output and a sum output, connections between said diodesand said 'relay tube, a calibrated network, an ampliierA the gain-ofwhichis adjustable coupled to 'said network,- a modulation meter coupledto said amplifier, and a switch for applying the differential 'outputofsaid diodes to said network whenv the instantaneous4 frequency of thewave energy is modulated or the sum output of said diodes'tol saidv.network when vthe amplitude of thewave energy. is' modulated.

8." In=a systemfor vanalyzing wave energy lmodulatedini phase -orfrequency or amplitude, a relay tube'ex'cited byl said modulated waveenergy, connections to said tube .for'operating the same as 'anamplitude limiter when the Wave is modulated in'fphase orfrequency'or asa coupling tube only when the fwave energy is amplitude modulated, amodulated Wave energy, demodulator comprising? ai frequency responsivecircuit coupled tosaid" tube, two rectiers coupled to said frequency.responsive circuit, impedances connectedl to said rectiiiers4 forcombining the recti- 4lier-outputs differentially when a phase orfrequencymod'ulated wave is being received or additiv'elyl when'anlamplitude modulated'wave is being-received; a Icalibrated amplifler, anattenuation network-at the inputfthereof, connectionsbetween-'lsaid'network and saidirnpedances and a' metercoupled to theroutput of said amplifier.

9. In asyst'em'for analyzing wave energy modulated in phase-or frequencyor amplitude, a relay tubeexcited 'by said-modulated wave energy,connection'sto said'tube for operating'the same as' anamplitudelimiter-when the wave is modulated in phase'or'frequency or-as acoupling tube only when the wave energy is amplitude modulated,v a'modulated wave-energy demodulator comprising a frequency responsive!circuit` coupled to saidtube; tw'o'rectlers coupled to'said frequencyresponsive circuit, imp'edances connected to said rectifiers forlcombining' the rectifier outputs, differentially when lphase orfrequency modulated'waves arebeing received' or additively whenamplitude modulated waves are being received, acoupling tube having anVinput to be excited by the differential or the additive output of saidrectiflers, a meter coupled to said coupling tube, an amplifier ofadjustablegain, a calibrated attenuatlon network at A the input thereof,connections' between s'aid networkf and said coupling tube arid-aAVmeter coupled to' thev output of said amplifier-l 10. Iii-a' system-for'metering wave energy the instantaneous' frequency or th'e amplitude ofwhichv is'l modulated inv accordance with signals, two electrondischarge' systems each'V having input and output electrodes including asource of electrons,I a common impedance connected between yelectrodesof said systems, connections for impressing the waves to be translatedon the input electrodes of one of said systems, connections forsupplying operating potential to the anode electrodesof said systems, aswitch for interrupting said supply to at least one anode electrode whenthe wave energy is modulated in amplitude, a pair of diode rectierscoupled to the output electrodes of the other of said electron dischargesystems, impedances connected to said diodes for differentially oradditively combining the rectied components, a coupling tube of thecathode follower type having an impedance in its cathode circuit,connections including a switch for applying the differential or sumoutput of the rectiiiers to said coupling tube, a meter coupled to saidlast-named impedance, a calibrated attenuation network coupled to saidlast-named impedance and a meter coupled by an amplifier of known gainto said calibrated network.

1l. In a system for analyzing wave energy modulated in phase orfrequency or amplitude, a modulated wave energy detector comprising afrequency responsive circuit, a pair of rectiers coupled to saidcircuit, impedances wherein the sum and the dierence of the separaterectiiier outputs appear, an amplifier tube having input and outputelectrodes, connections including a switch for impressing the sum ordifference of the rectier outputs on said input electrodes, a calibratednetwork coupled to said output electrodes, a meter, and an amplier ofadjustable gain coupling said meter to said network.

l2. In a system ci the class described, a converter tube having an anodeand a cathode and having a control grid excited by current to beconverted in frequency, an amplifier having circuits tuned to a xedfrequency and coupled to said converter, an oscillation generator thefrequency of which may be changed in steps through a given range, and afrequency multiplier operative to produce at least one harmonic of thegenerated frequency coupling said oscillation generator to a controlelectrode of said converter tube, the steps through which the frequencyof said generator may be changed being such that said currents excitingsaid control grid may fall in several frequency bands and yet providecurrent to said amplifier of a frequency within the range to which it istuned.

13. The method of relaying wave energy the amplitude or theinstantaneous frequency of which is varied in accordance with signals bymeans of two electron discharge systems each having an anode, a cathodeand a grid, and having a common cathode resistance which includes thesesteps, applying the wave energy to be relayed to the grid of one of saiddischarge systems, applying the potential drop in said resistance to thegrid of said other system, applying positive direct current potentialsto the anodes of both of said systems with respect to their cathodeswhere the wave energy being relayed has its instantaneous frequencymodulated so that wave energy amplitude limiting takes place during therelaying process, applying a direct current positive potential only tothe anode of said other system relative to its cathode where the waveenergy being relayed is amplitude modulated so that wave energy-relayingtakes place without material amplitude limiting and deriving the relayedwave energy from the anode of the other system.

14. The method of relaying wave energy modulated in amplitude or as toinstantaneous frequency in accordance with signals by means of twoelectron discharge systems each including a source of electrons, acontrol grid and an anode, an impedance having a terminal connected tothe electron emission source of both systems, a second impedancecoupling said rst impedance to the grid of one system, and a directconnection between the said other terminal and the control grid of theother system, which includes these steps, impressing the modulated wavesto be relayed on the control grid of said one system, deriving therelayed waves from the anode and cathode of the other of said systems,supplying direct current potential of the anodes of both of said systemswhere the instantaneous frequency of the wave energy is modulated sothat wave energy amplitude limiting takes place during the relayingprocess, and supplying direct current potential to the anode of one onlyof said systems where the wave energy is modulated in amplitude so thatwave energy relaying takes place without material amplitude limiting.

MURRAY G. CROSBY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,396,030 Dubilier Nov. 8,19211,592,937 Jammer July 20,1926 1,864,543 Horton June 28, 1942 2,021,692Lewis Nov. 19, 1935 2,022,067 Wheeler Nov. 26, 1935 2,035,745 GeorgeMar. 31, 1936 2,069,518 Chittick Feb. 2, 1937 2,145,371 Reid Jan.31,1939 2,276,565 Crosby Mar. 17, 1942 2,296,090 Crosby Sept. 15,19422,309,431 Summerhayes, Jr. Jan. 26,1943

the other terminal of

